The invention relates to a coupling sleeve for receiving a coupling plug. The two parts, together, form a hydraulic coupling and serve to connect two hydraulic pipes. The coupling sleeve is connected to a housing and includes a receiving chamber which secures and receives a coupling plug. The housing is associated with a valve. The valve establishes a connection with the receiving chamber and can be transferred into an open position. The receiving chamber is associated with sealing means to achieve a sealing effect relative to the coupling plug.
A hydraulic coupling with a coupling sleeve is described in DE 43 18 840 C2. The coupling has a switching pin which axially projects into the receiving chamber of the coupling sleeve and penetrates same when the coupling is switched into the open position. A manual lever is provided to open the coupling, with the housing which is connected to the coupling sleeve. The lever, via further elements, mechanically displaces the switching pin in the axial direction. The receiving chamber of the coupling sleeve is designed such that both a standard plug according to ISO 5675 and SAE-J 1036 and a special flat valve plug can be coupled and then opened by the switching pin. The flat valve plug is a plug which includes an end face which is planar and is arranged close to the bore end of the receiving chamber and also close to the end face of the valve. The flat valve plug is advantageous during uncoupling the coupling plug from the coupling sleeve in that any leakages are kept to a minimum. Even when using a standardized plug according to the above-mentioned standards, the oil leakage rate is still smaller than in cases where the valve is moved into the open position by inserting the coupling plug. In particular, such hydraulic couplings are used in agricultural machinery or in mobile hydraulic systems. Therefore the coupling sleeve has to be designed such that both standard plugs, and specially adapted plugs, with flush contact conditions, can be used to reduce the oil leakage rate. However, the disadvantage of the above design is that only one sealing assembly is selected for sealing the different types of coupling plugs. This means that, for example, plugs which provide a flat contact, e.g. whose end face is moved close to the end face of the receiving chamber and thus close to the valve, as a result of the compression of the enclosed air, are difficult to insert before establishing contact, e.g. before their end face rests against the end face of the receiving chamber.